rewrite icinga2* resources

[vkhatri]

Currently, each defined resource iterates over all icinga2 resources to format the final template file objects. It causes slowness for the larger objects/resources.

A possible solution is to modify https://github.com/Icinga/chef-icinga2/blob/master/libraries/provider_instance.rb#L26 to prevent resources iteration for each defined resource.

Also, it is worth considering Chef LWRP resources too. But, not sure how it will affect the template/zone/object formation.